Some tests abort in debug mode on `ubuntu-26.04`

[cqc-alec]

https://github.com/Quantinuum/tket/actions/runs/28235360965/job/83661263696?pr=2192 :

/usr/include/c++/15/bits/stl_vector.h:1346: constexpr std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::front() [with _Tp = unsigned int; _Alloc = std::allocator<unsigned int>; reference = unsigned int&]: Assertion '!this->empty()' failed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test-tket is a Catch2 v3.15.1 host application.
Run with -? for options

-------------------------------------------------------------------------------
Scenario: Small sets of Gadgets are partitioned correctly
      Given: No gadgets
-------------------------------------------------------------------------------
/home/runner/work/tket/tket/tket/test/src/test_Partition.cpp:35
...............................................................................

/home/runner/work/tket/tket/tket/test/src/test_Partition.cpp:35: FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGABRT - Abort (abnormal termination) signal

===============================================================================
test cases:    463 |    462 passed | 1 failed
assertions: 322785 | 322784 passed | 1 failed

Aborted (core dumped)

https://github.com/Quantinuum/tket/actions/runs/28242245028/job/83672227673?pr=2192 :

/usr/include/c++/15/bits/stl_vector.h:1263: constexpr std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = boost::detail::adj_list_gen<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>, boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>::config::stored_vertex; _Alloc = std::allocator<boost::detail::adj_list_gen<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>, boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>::config::stored_vertex>; reference = boost::detail::adj_list_gen<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>, boost::vecS, boost::vecS, boost::bidirectionalS, tket::Node, tket::graphs::WeightedEdge, boost::no_property, boost::listS>::config::stored_vertex&; size_type = long unsigned int]: Assertion '__n < this->size()' failed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test-tket is a Catch2 v3.15.1 host application.
Run with -? for options

-------------------------------------------------------------------------------
Scenario: LinePlacement class
      Given: Empty circuit, two qubit Architecture, LinePlacement::Place.
-------------------------------------------------------------------------------
/home/runner/work/tket/tket/tket/test/src/Placement/test_LinePlacement.cpp:26
...............................................................................

/home/runner/work/tket/tket/tket/test/src/Placement/test_LinePlacement.cpp:26: FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGABRT - Abort (abnormal termination) signal

===============================================================================
test cases:    452 |    451 passed | 1 failed
assertions: 705418 | 705417 passed | 1 failed

Aborted (core dumped)